Balance of probabilities or loss of a chance?

A landmark Supreme Court judgment in a professional negligence claim was handed down on 13 February 2019 – Perry v Raleys Solicitors [2019] UKSC.

Raleys Solicitors, represented by Michael Pooles QC and Ben Quiney QC, were victorious in overturning the judgment of the Court of Appeal.

The approach adopted in a particular case will determine how much the financial loss is. If the test applied is balance of probabilities it is basically ‘all or nothing’ whereas assessment of a lost chance will result in a percentage being applied to the sum claimed.

The explanation of the difference is explained as follows:

Commonly, the main difficulty arises from the fact that the court is required to assess what if any financial or other benefit the client would have obtained in a counter-factual world, the doorway into which assumes that the professional person had complied with, rather than committed a breach of, his duty of care.

The everyday task of the court is to determine what, in fact, happened in the real world rather than what probably would have happened in a what-if scenario generally labelled the counter-factual.

Similar difficulties arise where the question of causation or assessment of damage depends upon the court forming a view about the likelihood of a future rather than past event.

In both those types of situation (that is the future and the counter-factual) the court occasionally departs from the ordinary burden on a claimant to prove facts on the balance or probabilities by having recourse to the concept of loss of opportunity or loss of a chance.

(paragraphs 16 and 17 of the judgment of Lord Briggs: unanimously agreed)